Quote from abattia:
"Kelly Criterion ... a mathematical formula relating to the long-term growth of capital... currently used by gambers and investors to determine what percentage of their bankroll/capital should be used in each bet/trade to maximize long-term growth.
Kelly % = W - [(1-W)/R]
... there are two key components to the formula: the winning probability factor (W) and the win/loss raion (R)...
[Investopedia.com]
W = 5/6
R = 2
----> Kelly % = 75%
Are you sure about R in this case? Double or nothing is 1 to 1 payout or 2 for 1, not 2 to 1. i.e. R should be 1, and based on Kelly criterion the fraction would be 33%